The present invention relates generally to current sensing amplifiers, and more particularly to a current sensing amplifier which is capable of accurately sensing current flowing through a trace conductor on a printed circuit board (PCB) and providing instant, automatic temperature compensation of the sensed value by means of a gain resistor that is included within the current sensing amplifier and is composed of essentially the same kind of material as the trace conductor.
It would be desirable to have a highly accurate current sense amplifier that can be used when there is a need for precise measurement of current flowing in a PCB conductor. Furthermore, even if a particular application does not require accurate measurement of the amount of current flowing into a load to accomplish a primary function of the application, it nevertheless often is desirable to have an accurate, temperature-compensated value representing the voltage drop in a copper trace conductor of a PCB in order to detect an overload condition so that appropriate steps can be taken to avoid damage from being caused by the overload condition.
The closest known current sensing amplifier, shown in subsequently described Prior Art FIG. 1, requires complex circuitry and an associated method of temperature-compensating a voltage drop across the shunt resistor, by (1) sensing the voltage drop across the shunt resistor, (2) generating a signal representative of the shunt resistor temperature by means of a temperature sensor, and (3) externally digitizing and using that temperature signal to temperature-compensate an externally digitized representation of the sensed voltage drop across the shunt resistor by means of expensive and time-consuming digital techniques, for example by means of a microcontroller.
The closest prior art is believed to be shown in the published data sheet entitled “IA2410 High Voltage, High-Side Current Sense Amplifier” (date unknown), published by Integration Associates, Inc. of Mountain View, Calif. Prior Art FIG. 1 shows a functional block diagram of the current sense amplifier 2 in the above mentioned data sheet. Referring to Prior Art FIG. 1, the circuitry 1A includes the IA2410 current sense amplifier 2 connected to measure the voltage across a shunt resistor 6, which is illustrated as being on a printed circuit board 3. Printed circuit board 3 includes application circuitry 4 connected by a copper trace conductor 5 to one terminal of shunt resistor 6, which has a resistance RSHUNT. The other terminal of shunt resistor 6 is connected by copper trace conductor 5A to load circuitry 8, which can be located on or off printed circuit board 3. The above mentioned data sheet reference suggests that shunt resistor 6 could possibly be a section of the copper trace conductor 5,5A.
Conductor 5 in Prior Art FIG. 1 is coupled by a first gain resistor RG2 to the (+) input of an operational amplifier 9 in current sense amplifier 2, which also includes a variable current source 11, a temperature sensor 14, a switch 15, a buffer 16, and a control circuit 17. Conductor 5A is coupled by a second gain resistor RG1 to the (−) input of operational amplifier 9, the output of which is coupled by conductor 10 to the control input of variable current source 11. The upper terminal of variable current source 11 is connected to the (+) input of operational amplifier 9, and the lower terminal of variable current source 11 is coupled by means of a switch 20 to an output conductor 12 on which an output voltage is produced. Output conductor 12 is connected to one terminal of an output resistor 13 and also to the output of a buffer circuit 16. The input of buffer 16 is connected to one terminal of a switch 15, the other terminal of which is connected to the output of a temperature sensor 14.
The output of temperature sensor 14 and the output of the current source 11 representing the voltage across RSHUNT can be selectively applied to Vout conductor 12 by means of control circuit 17, switch 15, switch 20, and buffer circuit 16. The output of temperature sensor 14 thereby can be provided as an input to buffer circuit 16, the output of which can be digitized and used externally to temperature-compensate a digitized representation of the load current through RSHUNT. Control circuit 17 can control when each of the lower terminal of current source 11 and the output of temperature sensor 14 are operatively coupled, one at a time, to Vout conductor 12.
The use of current sensing amplifiers to accurately sense the voltage drop across a portion of a copper trace on a printed circuit board over a normal operating temperature range of −40 to +125 degrees Centigrade is problematic because this involves difficult trade-offs. Copper is a high-conductivity metal conductor rather than a resistive material, so a section of a conventional printed copper trace conductor would need to be very long (and perhaps configured in a serpentine pattern) in order to have a sufficiently high resistance to be usable as a shunt resistor for a conventional current sense amplifier. Use of a portion of a typical PCB copper trace conductor as a shunt resistor generally has been considered to be impractical because it would require a large and costly amount of PCB area.
Thus, there is an unmet need for an integrated circuit current sensing amplifier which makes it practical to provide very low cost, very accurate sensing of current flowing through a printed circuit board conductor.
There also is an unmet need for an integrated circuit current sensing amplifier which makes it practical to provide very low cost, very accurate sensing of current flowing through a printed circuit board conductor without requiring use of a temperature-sensing element.
There also is an unmet need for an integrated circuit current sensing amplifier which makes it practical to provide very low cost, very accurate sensing of a voltage developed across a portion of a printed circuit board conductor used as an external shunt resistance in response to a load current flowing through the printed circuit board conductor, wherein the current sensing amplifier provides simple, instant temperature compensation of the sensed voltage.
There also is an unmet need for an integrated circuit current-sensing amplifier which avoids the external digitizing and computation which the prior art requires to temperature-compensate the measured voltage across a shunt resistor.